Twitter should put some effort into moderating such phishing ads and think about the safety of their users.
They don't think about users' safety. Twitter is one of the uncensored social media pornstars who post porn videos and they do nothing. It cannot be a
social media. Not only Twitter but Facebook also approves such ads which contain phishing links.
But as far as I think Twitter will not remove these scam/phishing ads until they face any legal problem.
Even if they face legal problems, they might fight against it saying the users should report the phishing links to co-operate with them. They can't check each service before they approve the ads. Afterall, they have a back. But Bitcointalk forum does not have their back which is the reason they are censoring the mixers.